Yesterday we reviewed a study published one year ago which concluded that the total loss of Arctic summer sea ice would result in a temperature increase equal to 0.19C, which will be added bit by bit to the annual average increase for the entire globe. Actual increases would be much higher than this in certain regions, largely confined to Arctic locations over a limited number of months. You need to recognize that the Arctic Circle contains only about 4% of the Earth’s total surface area. Now I have found another study covering the same subject, published two years ago by a different group using different methods. This group came up with the very same conclusion: +0.19C for the average global effect of a full summer meltdown. The study also had other interesting things to say, which are worthy of some extra comment. You can also read the full report at this link: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL082914.
Quoting from the report, with my comments italicized: “The disappearance of sea ice alters the Earth’s energy balance because a low-albedo open ocean surface typically absorbs approximately 6 times more solar radiation than a surface covered with sea ice and snow…..” This is the most basic reason for the warming, all of it solar by origin 2. “The observed Arctic sea ice retreat per degree of global warming is 2.1 times larger than the CMIP5 ensemble-mean result, with no model simulating a value as extreme as the observations…..This suggests that there may be substantial systematic biases in the model projections of the level of global warming at which the Arctic becomes annually ice free.” Current models used in temperature forecasting are said to be badly off base, and behind the curve, with respect to both extent and timing of the heating impact. 3. “Of the 0.71 W/m2 of globally averaged heating, 0.21 W/m2 is estimated to have already occurred between 1979 and 2016.” Bringing everything up to date, this would suggest that about 40% of the warming effect has already been realized, leaving a little over 0.1C still to come. 4. “This heating of 0.71 W/m2 is approximately equivalent to the direct radiative effect of emitting one trillion tons of CO2 into the atmosphere… As of 2016, an estimated 2.4 trillion tons of CO2 have been emitted since the preindustrial period…..Arctic sea ice would be equivalent to 25 years of global CO2 emissions at the current rate.” What an interesting comparison! Also, as you well know, about one half of all CO2 emissions are absorbed by land or sea and do not end up in the atmosphere. Warming due to sea ice loss has much less ability to hide.
Global average temperatures have been rising at a rate of 0.16C per decade for the last five decades. The complete summer loss of Arctic sea ice, at 0.19C, would be equal to twelve years worth of warming—at this rate—all by itself. The effect can be created only once, and must then keep repeating every summer. Many close observers have been saying we will reach that unhappy goal within two decades, which I think is quite possible. Then what? Are there any feedbacks or chain reactions that need to be considered? For one, Arctic Ocean water will be collecting and storing part of that new summer energy input every year thereafter. It will be there, in the water, to a growing extent all winter long, helping to thin down the winter ice everywhere and nibbling away at its margins. Any amount of additional open water created during any of the long winter months is sure to add several degrees to air temperatures in the immediate area, and these gains are likely to add up over the years, or for as long as summers are warm. (Some of these local anomalies can be seen today.)
I am thinking also of another feedback that does not get much attention in the science literature but has been described many times in previous letters. This is the effect that Arctic surface warmth has on the formation of air pressure regularity in the upper atmosphere. The next two images show you what is happening to the configuration of these pressures in the NH compared with the SH. Both configurations are created in response to the pattern of temperatures that exist at each surface, based on thermal expansion rates applicable to actual air temperatures found in all different localities. The blue zone in the NH should be larger and more compact than it is now, meaning more like the one in the SH, this late in the fall. Having so much irregularity results in a highly confused pattern of jetstream wind pathways, which at all times are governed by the continuous courses taken (as isobars) by air pressure differentials. This confusion allows more of the precipitable water (PW) content of atmospheric rivers to wander deeply into the polar region, adding to local greenhouse energy effects in an anomalous way when it does so. The overall result is a mutually reinforcing feedback loop between surface temperatures and the extent of PW migration. For the benefit of new readers, I need to go back and reopen the explanation for all this activity in greater detail.
Carl